Combinational probability

Comb.hs

import Debug.Trace
import System.Environment

qnr :: Integer -> Integer -> Double -> Double
qnr n r 0 = 0
qnr n r p
  | n < r     = 0
  | n == r    = q
  | otherwise = q + (n' - r')*(log(1-p)) + (foldl (+) 0 (map (log) [n'-r'+1..n'])) - (foldl (+) 0 (map log [2..r']))
  where n' = fromIntegral n
        r' = fromIntegral r
        q = r' * (log p)

exp_qnr :: Integer -> Integer -> Double -> Double
exp_qnr n r p = exp (qnr n r p)

pnr :: Integer -> Integer -> Double -> Double
pnr n r 0 = 0
pnr n r p
  | n < r     = 0
  | n == r    = exp q
  | otherwise = pnr (n-1) r p + p * exp_qnr (n-1) (r-1) p
  where q = fromIntegral r * (log p)

main = do
  args <- getArgs
  (n,r,p) <- case args of
    n':r':p':_ -> (,,) <$> readIO n' <*> readIO r' <*> readIO p'
    _ -> return (6400, 64, 0.8)
  -- putStrLn $ "qnr " ++ show n ++ " " ++ show r ++ " " ++ show p ++ " = " ++ show (exp_qnr n r p)
  putStrLn $ "pnr " ++ show n ++ " " ++ show r ++ " " ++ show p ++ " = " ++ show (pnr n r p)